Magnetic sensor with high and low resolution tracks

ABSTRACT

A sensing apparatus that includes first and second magnet assemblies. The first magnet assembly includes first and second magnets that have respective first and second opposite magnetic fields, and respective first and second dimensions. The first dimension is relatively smaller than the second dimension. The second magnet assembly is positioned at a distance from the first magnet assembly. The second magnet assembly includes a third magnet that has a third magnetic field which is opposite to the first magnetic field.

RELATED APPLICATION

This application claims the benefit of U.S. Provisional Application Ser.No. 60/758,333, filed on Jan. 12, 2006, the entire content of which isincorporated by reference herein.

FIELD

Embodiments of the invention relate generally to magnetic sensors, andparticularly to magnetic sensors with high and low-resolution tracks.

BACKGROUND

Magnetic position sensors generally have two or more magnetic tracks.Each magnetic track accounts for a specific magnetic resolution, such asa high and low-resolution, and consists of a number of electromagneticfield generating magnets. These magnetic position sensors typicallyrequire a gap between the magnetic tracks in order to reduce magneticcrosstalk between the tracks. However, if the gap between the tracks isnot sufficiently large, magnetic fields generated by the separatemagnetic tracks interact with each other. As a result, accuracy of thesensors is compromised. On the other hand, while a large gap between themagnetic tracks reduces the magnetic crosstalk, the resulting magnettracks are typically larger.

More particularly, the magnets of a high-resolution track are generallyinfluenced by the magnets of a low-resolution track. For example, theSouth field of a low-resolution track that is adjacent to sections of ahigh-resolution track will superimpose a North field on the sections ofthe high-resolution track. In such cases, the superimposed North fieldwill result in wider North poles of the high-resolution track than theSouth poles at zero crossings of the field generated by the magnets ofthe high-resolution track. The zero crossings generally represent amagnetic field strength generated by the magnets of the high-resolutiontrack measured at different angular positions around the high-resolutiontrack. Similarly, the North field of a low-resolution track that isadjacent to sections of a high-resolution track will superimpose a Southfield on the sections of the high-resolution track. In such cases, thesuperimposed South field will result in wider South poles of thehigh-resolution track than the North poles at the zero crossings of thefield generated by the magnets of the high-resolution track.

SUMMARY

In one form, the invention provides a sensing apparatus that includesfirst and second magnet assemblies. The first magnet assembly includesfirst and second magnets that have respective first and second oppositemagnetic fields, and respective first and second dimensions. The firstdimension is relatively smaller than the second dimension. The secondmagnet assembly is positioned at a distance from the first magnetassembly, and includes a third magnet. The third magnet has a thirdmagnetic field that is opposite to the first magnetic field.

In another form, the invention provides a sensing apparatus thatincludes high and low-resolution tracks. The low-resolution trackincludes a first magnet that has a first magnetic pole, and a firstcircumferential dimension. The high-resolution track is spaced apartfrom the low-resolution track, and includes a second magnet that has asecond circumferential dimension and a magnetic pole which issubstantially identical to the first magnetic pole. The high-resolutiontrack also includes a third magnet that has a third circumferentialdimension. The third circumferential dimension is different from thesecond circumferential dimension. The third magnet also has a thirdmagnetic pole that is opposite to the first magnetic pole.

In yet another form, the invention provides a sensing apparatus thatincludes high and low-resolution tracks, and an opposite-field track.The low-resolution track includes a first magnet that has a firstmagnetic pole. The high-resolution track circumferentially surrounds thelow-resolution track, is spaced apart from the low-resolution track by afirst gap, and has a circumferential dimension. The high-resolutiontrack includes a second magnet that has a magnetic pole which issubstantially identical to the first magnetic pole, and a third magnetthat has a third magnetic pole which is opposite to the first magneticpole, and a pole superimposed from the first magnet. The opposite-fieldtrack also circumferentially surrounds the high-resolution track, isspaced apart from the high-resolution track by a second gap, andincludes a fourth magnet having a fourth magnetic pole that issubstantially identical to the first magnetic pole to reduce thesuperimposed pole from the first magnet.

Other aspects of the invention will become apparent by consideration ofthe detailed description and accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top schematic view of a sensing apparatus having high andlow-resolution tracks.

FIG. 2 is a detailed top schematic view of a plurality of sections ofthe sensing apparatus of FIG. 1.

FIG. 3 is an exemplary wedge-shaped magnet used in the high andlow-resolution tracks of FIG. 1.

FIG. 4 is a top schematic view of an alternative sensing apparatus.

FIG. 5A is a side schematic view of a motor cap.

FIG. 5B is a bottom schematic view of the motor cap of FIG. 5A.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description or illustrated in the following drawings.The invention is capable of other embodiments and of being practiced orof being carried out in various ways. Also, it is to be understood thatthe phraseology and terminology used herein are for the purpose ofdescription and should not be regarded as limiting. The use of“including,” “comprising,” or “having” and variations thereof herein ismeant to encompass the items listed thereafter and equivalents thereofas well as additional items. Unless specified or limited otherwise, theterms “mounted,” “connected,” “supported,” and “coupled” and variationsthereof are used broadly and encompass both direct and indirectmountings, connections, supports, and couplings. Further, “connected”and “coupled” are not restricted to physical or mechanical connectionsor couplings.

Embodiments of the invention will also be described with reference tothe accompanying drawing figures wherein like numbers represent likeelements throughout. Certain terminology, for example, “top,” “bottom,”“right,” “left,” “front,” “frontward,” “forward,” “back,” “rear,” and“rearward,” is used in the following description for relativedescriptive clarity only and is not intended to be limiting.

Embodiments of the invention relate to a sensing apparatus with high andlow-resolution tracks. In some embodiments, the high-resolution trackincludes magnets of different dimensions that have opposing magneticfields. The low-resolution track includes magnets of similar dimensions.Some of the magnets of the low-resolution track have magnetic fieldsthat are opposite to the magnetic fields generated by some of themagnets of the high-resolution track, and therefore superimpose magneticpoles on the high-resolution track. Magnetic poles that are opposite tothe superimposed magnetic poles are generated in the high-resolutiontrack to cancel or compensate for the superimposed magnetic poles. Inone embodiment, the dimensions of some of the magnets of thehigh-resolution track are configured to be relatively smaller than thedimensions of the other magnets of the high-resolution track tocompensate for the magnetic fields generated by the magnets of thelow-resolution track. In this way, effects due to the superimposed fieldcan be canceled or reduced such that the North poles and the South poleshave similar zero crossings.

Embodiments of the invention also provide a sensor apparatus includinghigh and low-resolution tracks. Each of the tracks consists of aplurality of magnets, and each of the magnets generates a magneticfield. As a result, each of the tracks has an overall magnetic field andhence a magnetic field pattern.

In some embodiments, the magnetic field pattern of the high-resolutiontrack is generally structured to compensate for a North pole that issuperimposed on the high-resolution track. FIG. 1 shows a top schematicview of a magnetic sensing apparatus 100 having a high-resolutionassembly or track 104 and a low-resolution assembly or track 108. Anexemplary magnetic sensing apparatus is a positional and directionalsensing system incorporated in a motor. The high and low-resolutiontracks 104, 108 are separated by a gap 112. While the South pole of amagnet 116 of the low-resolution track 108 superimposes a North pole ona section 120 of the high-resolution track 104, magnets of the section120 are configured such that effects of the superimposed North pole arereduced or minimized. Similarly, while a North pole magnet 132 of thelow-resolution track 108 superimposes a South pole on a section 136 ofthe high-resolution track 104, magnets of the section 136 are configuredsuch that effects of the superimposed South pole are reduced orminimized.

Although the high and low-resolution tracks 104, 108 are shown ascircular in shape, the high and low-resolution tracks 104, 108 can alsohave other shapes, such as elliptical shapes, polygonal shapes, and acombination thereof. Furthermore, although one low-resolution track 108and one high-resolution track 104 are shown in FIG. 1, the sensingapparatus 100 can also include multiple high-resolution tracks, multiplelow-resolution tracks, and/or a combination of multiple high andlow-resolution tracks.

FIG. 2 shows a detailed top schematic view of exemplary sections 120,136 of the high-resolution track 104. Particularly, magnets 124 of thehigh-resolution track 104 that have an associated North pole aregenerally narrower than magnets 128 of the high-resolution track 104that have an associated South pole, which will be detailed below.Similarly, magnets 140 of the high-resolution track 104 that have anassociated South pole are generally narrower than magnets 148 of thehigh-resolution track 104 that have an associated North pole, which willbe detailed below. FIG. 2 also shows that the magnets 124 near a center184 of the section 120 are narrower than the magnets 124 away from thecenter 184 of the section 120 to provide more compensation near thecenter 184 of the section 120. Similarly, FIG. 2 also shows that themagnets 140 near a second center 188 of the section 136 are narrowerthan the magnets 140 away from the second center 188 of the section 136to provide more compensation near the second center 188 of the section136. Although the magnets 124, 128, 140, 148 are shown as wedge-shapedmagnets, the magnets 124, 128, 140, 148 can also have other suitableregular or irregular shapes. Furthermore, the magnets 124, 128, 140, 148can include a combination of permanent magnets, temporary magnets,electromagnets, and the like that are made of different materials, suchas neodymium iron boron (“NdFeB” or “NIB”), samarium cobalt (“SmCo”),alnico, ceramic, ferrite, and the like.

In the embodiment of FIG. 2, the circumferential dimensions of magnetsare reduced to minimize or reduce the magnetic pole effect. Otherdimensions and parameters of the magnets of the high-resolution track104 can be adjusted or structured such that there is an opposite,compensating, or canceling pole in the high-resolution track 104. Forexample, to provide more compensation near the center 184 of the section120, the magnets 124 that have the superimposed poles in thehigh-resolution track 104 can be axially thinner near the center 184 andan axis that is parallel to an axis 192 of the high-resolution track 104than the magnets 124 that are away from the center 184 of the section120. In such embodiments, the magnets 124 that have the superimposedpoles in the high-resolution track 104 can also be axially thinner thanthe adjacent magnets 128 to provide compensation for the section 120.Alternatively, to provide more compensation near the center 184 of thesection 120, the magnets 124 that have the superimposed poles in thehigh-resolution track 104 can be radially smaller near the center 184and along a diameter 194 than the magnets 124 that are away from thecenter 184 of the section 120. In such embodiments, the magnets 124 thathave the superimposed poles in the high-resolution track 104 can also beradially smaller than the adjacent magnets 128 to provide compensationfor the section 120. In other embodiments, the magnets 124 can bestructured to radiate a magnetic field that is weaker in magnetic fieldstrength than that of the adjacent magnets 128.

FIG. 3 shows an exemplary wedge-shaped magnet 200 that can be used asthe magnets 124, 128, 140, 148 of the high-resolution track 104 in FIG.2. The magnet 200 has an interior or inner circumferential dimension 204along a first circumferential portion 208 of the magnet 200, and anexterior or outer circumferential dimension 212 along a secondcircumferential portion 216. The magnet 200 also has an exterior orouter axial dimension 220 along an exterior axial edge 224 of the magnet200, a second interior or inner axial dimension 228 along an interioraxial edge 232 of the magnet 200, and a radial dimension 236 along aradial edge 240. Although the exterior axial dimension 220 and thesecond interior axial dimension 228 are shown as substantially equal inFIG. 3, the exterior axial dimension 220 and the second interior axialdimension 228 can be different in some other embodiments to providemagnetic pole compensation as desired. For example, to compensate for asuperimposed magnetic pole, the exterior axial dimension 220 can besmaller than the second interior axial dimension 228 to lessen therespective magnetic field strength. Furthermore, as described, tocompensate for the superimposed poles at the sections 116, 136, themagnets 124, 140 are narrower than the respective magnets 128, 148. Insome embodiments, to compensate for the superimposed North pole at thesection 116 (of FIG. 1), the inner circumferential dimension 204 of themagnets 124 is smaller than the inner circumferential dimension 204 ofthe magnets 128. The outer circumferential dimension 212 of the magnets124 is also smaller than the outer circumferential dimension 212 of themagnets 128. Similarly, to compensate for the superimposed South pole atthe section 136 (of FIG. 1), the inner circumferential dimension 204 ofthe magnets 140 is smaller than the inner circumferential dimension 204of the magnets 148. The outer circumferential dimension 212 of themagnets 140 is also smaller than the outer circumferential dimension 212of the magnets 148.

FIG. 4 shows a top schematic view of an alternative sensing apparatus400. The sensing apparatus 400 includes a low-resolution track 404, anda high-resolution track 408 that are separated by a first gap 413. Thesensing apparatus 400 also includes a compensation track 412 that isseparated from the high-resolution track 408 by a second gap 409. Thehigh-resolution track 408 has an interior circumference 410 thatcircumferentially surrounds the low-resolution track 404. Magnets 416have essentially the same dimensions throughout the high-resolutiontrack 408. As described earlier, the high-resolution track 408 isinfluenced by magnets 420 of the low-resolution track 404. Thecompensation track 412 circumferentially surrounds the high-resolutiontrack 408 on an outer circumference 422. Particularly, the compensationtrack 412 provides a field of equal strength but opposite fielddirection relative to the field generated by the low-resolution track404. The compensation track 412 generally includes a plurality ofmagnets 424 that generate an opposite field than the field generated bythe magnets 420 of the low-resolution track 404 as described. Becausethe compensation track 412 is near the high-resolution track 408 and thelow-resolution track 404, the magnetic field generated by the magnet 420and superimposed on the magnets 416 of the high-resolution track 408 isnearly or completely canceled by the opposite field generated by themagnets of the compensation track 412. That is, a net field effect ofzero or near zero from the low-resolution track 404 is measured at thehigh-resolution track 408.

Embodiments herein can be used to detect steering wheel position orwheel position, and can be used in other critical angle position sensingapplications, robotic applications, packaging applications, andmanufacturing assembly applications. Furthermore, embodiments herein canbe used in other equipment, such as agricultural equipment, earth movingequipment, off-road equipment, forklifts, and on-road vehicles.

FIG. 5A and FIG. 5B respectively show a side view and a bottom view of acap 500 of a motor (not shown). The sensing apparatuses 100, 400 can beincorporated in the motor near the cap 500. The motor cap 500 includes aprinted circuit board 504 that includes a high-resolution sensor 508 anda plurality of commutation sensors 512. In some embodiments, thehigh-resolution sensor 508 is positioned near the high-resolution track104, and the commutation sensors 512 are generally positioned near thelow-resolution track 108 to obtain approximate absolute positions of themotor. Particularly, the commutation sensors 512 can be generally phasedapart, such as by 120°. At startup of the motor, the commutation sensors512 are energized, and thus an approximate absolute position of thelow-resolution track 108 can be determined.

Thus, the invention provides, among other things, a sensing apparatus.

1. A sensing apparatus comprising: a first magnet assembly includingfirst and second magnets having respective first and second oppositemagnetic fields wherein the first magnet has a plurality of dimensionsincluding an inner circumferential dimension, an outer circumferentialdimension, an inner axial dimension, an outer axial dimension, and aradial dimension, and the second magnet has a corresponding plurality ofdimensions, and wherein the inner circumferential dimension or outercircumferential dimension of the first magnet is relatively smaller thanthe corresponding dimension of the second magnet; and a second magnetassembly circumferentially surrounded by the first magnet assembly andpositioned at a distance from the first magnet assembly, the secondmagnet assembly including a third magnet having a third magnetic fieldopposite to the first magnetic field.
 2. The sensing apparatus of claim1, wherein the first magnet assembly is a high-resolution track, andwherein the second magnet assembly is a low-resolution track.
 3. Thesensing apparatus of claim 1, wherein the first magnet assembly has amagnet section, the magnet section having a center, the first magnet ispositioned near the center, and the first magnet assembly furtherincludes a fourth magnet having a fourth magnetic field opposite to thesecond magnetic field, wherein the fourth magnet is positioned adjacentthe second magnet and away from the center, and has an outercircumferential dimension, wherein the outer circumferential dimensionof the first magnet is relatively narrower than the outercircumferential dimension of the fourth magnet, and wherein the magnetsection includes the first, second, and fourth magnets.
 4. The sensingapparatus of claim 3, further comprising: an opposite-field trackcircumferentially surrounding the first magnet assembly, spaced apartfrom the first magnet assembly by a second gap, and including a fifthmagnet having a fifth magnetic field that is opposite to the thirdmagnetic field, and configured to reduce a superimposed pole from thethird magnet.
 5. The sensing apparatus of claim 1, wherein the first,second, and third magnets are wedge-shaped.
 6. The sensing apparatus ofclaim 1, further comprising: at least one high-resolution sensorpositioned near the first magnetic assembly, and configured to sense aposition of at least one of the first and second magnets; and at leastone low-resolution sensor positioned near the second magnetic assembly,and configured to sense a position of the third magnet.